Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR TREATING MUDDY WATER
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates to a muddy water treating
method wherein coagulating agents are added to muddy
water to be treated to coagulate fine particles in muddy
water into large-sized solid flocs and more
particularly, to a -treating method suitably used for the
process of muddy water produced by the execution of a
tunnel~ing operation, a boring operation, a pile driving
operation, an operation of removing sedimentary earth in
a storage lake and sewage treatment or the like.
Description of the Prior Art:
A known method of ramoving fine particles from
muddy water comprises adding one or more coagulating
agents in muddy water in a treating vessel to combine
fine particles in the muddy water into flocs and
sedimentating the flocs by gravity. In this known method,
muddy wa~ter is separated into a floc phase and an aqueous
phase since the flocs are settled. The thus separated
flocs are removed from the treating vessel and dewatered,
i.e., dehydrated, and then wasted in position. In contrast,
the separated water is finally returned to
rivers.
In the known method, the coagulating agents are
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merel~ added, so that large-sized or hard flocs cannot be produced.
In most cases, fine particles are partially left in the liquid with
the great possibility that the separated water is not transparent.
If the formed flocs are small in size, they are liable to
run away along with the liquid at the time of dewatering or
transport of the flocs, thus leading to a troublesome after-
treatment of the flocs. Alternatively, if the flocs are soft with
their mechanical strength being small, the flocs are apt to break.
Especially, at the time of dewatering and transport, the flocs will
be broken into fine particles, so ~hat the broken flocs are run
away along with water. The opaqueness of the separated liquid
means that fine particles are left in the liquid with incomplete
removal of the fine particles.
Accordingly, the coagulating agents have been
conventionally added in large amounts, but the use of the large
amounts of expensive chemicals will require much treating costs.
Even if coagulating agents are used in large amounts under
conditions where the concentration of fine particles in muddy water
is high, either large-sized or hard flocs are not produced or the
resultant water becomes opaque.
To overcome the above disadvantages involved in high
muddy water concentration, it has been usual to add clear water to
muddy water so as to lower the concentration, after which
coagulating agents are added.
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However, the addition of clear water to the muddy water undesirably
increase the amount of the total water to be treated.
SUMMARY OF ~HE INVENTION
It is an object of the present invention to provide a
method for treating muddy water wherein large-sized and hard flocs
can be formed by the use of small amounts of chemicals and the
resultant water becomes clear and transparent.
The above object can be achieved, according to the
present invention, by a method for treating muddy water which
comprises adding to muddy water at least one of chemicals selected
from the group consisting of alkali metal oxides, alkaline earth
metal oxide, alkali metal hydroxides and alkaline earth metal
hydroxides so that the muddy water is rendered alkaline in pH,
adding an anionic polymer coagulant to the muddy water
simultaneously with or after the addition of the selected compound,
adding a sulfate to the muddy water so that muddy water is adjusted
to a weakly alkaline level, and then adding an anionic polymer
coagulant to the thus adjusted muddy water.
According to the present invention, by the addition of
the chemicals in the above order while adjusting the pH as defined
above, large-sized and hard flocs can be formed using small amounts
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of the chemicals, coupled with a further advantage that the
resultant water becomes transparent. The reason for this is
considered as follows.
In general, fine particles in the muddy water to be
treated are combined together and grow into flocs having a fair
size. The flocs are potentially stable, under which when
coagulants are added to the muddy water, the flocs are combined
into only slightly larger-size flocs.
In contrast, accordin~ to the present invention, since
the pH of the muddy water is adjusted to an alkaline level in the
pH by addition of an alkali metal oxide, alkaline earth metal
oxide, alkali metal hydroxide or alkaline earth metal hydroxide,
solid matters combined in the muddy water are deflocculated. By
this, the muddy water is converted into a state where flocculation
with polymer coagulant is effectively carried Ollt. In fact, the
addition of an anionic polymer coagulant at the same time or after
the conversion contributes to coagulation or part of the
deflocculated fine particles and fulvic acid in the muddy water.
In this condition, muddy matter remains in the muddy
water and humic acid is not deflocculated or dissolved therein.
Accordingly, a sulfate is added to the muddy water to adjust the pH
to a weakly alkaline level, so that humic acid is dissolved and
that hydroxide is produced. In this state, an anionic polymer
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coagulant is added to the resultant muddy water to cause remaining
fine particles such as of humic acid, the hydroxide and metal ions
to be combined, resulting in larger-sized and harder flocs.
The sulfate useful in the above step includes, for
example, aluminium sulfate, ferric sulfate and mixtures thereof.
The anionic polymer coagulants include, for example,
sodium alginate, sodium polyacrylate, maleate copolymers, partial
hydroly~ates of polyacrylamide and the like. In the practice of
the inventionf the anionic polymer coagulants may be used
singularly or in combination.
The pH adjusted by addition of the alkaline chemical is
generally a value greater than the pH value of the muddy water by
0.5 and the pH adjusted by addition of a sulfate should be weakly
alkaline and is in the range of from 7.0 to 7.3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is described by way of application
examples wherein the amounts of the respective chemicals were
minimized but optimum amounts which were determined according to a
preliminary test from which flocs and separated water were
optimumly obtained. Comparative Examples are also described.
Examples lA to lL
In each of Examples lA to lL, predetermined amount of
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caustic soda was added as chemical 1 to a muddy water produced
during excavation of gravel layer by means of a muddy water-type
tunnelling machine, so that the pH of the muddy water is adjusted
to value indicated in Table lA. Simultaneously, a partial
hydrolyzate of polyacrylamide (anionic polymer coagulant,
commercial name of DK Floc DK-10 available from Kurita Kogyo
Kabushiki Kaisha) having a molecular weight of about 107 was added
to the muddy water as chemical 2, followed by further addition of
aluminium sulfate as chemical 3 to the muddy water to adjust the pH
to 7.1 to 7.3 and also of an anionic polymer coagulant used as
chemical 1 to thP muddy water as chemical 4.
In each of Examples lA to lL, the concentration (%) of
fine particles in the muddy water, the pH of the muddy water after
the addition of the chemical 1 and the amounts (%) of the
respective chemicals per 100 ml of muddy water are shown in Table
lA.
The chemicals 1, 2, 3 and 4 were added as aqueous
solutions with concentrations of 1.0%, 0.2%, 20% and 0.2%
respectively. During the addition of all the chemicals, the muddy
water was agitated.
The water content (%) in flocs separated by filtrating
the coagulated muddy water, turbidity of the separated water and
the state of flocs (filter cakes) are shown in Table lA.
As a result, it was found from these Examples that large-
sized and hard flocs were formed with transparent separated water.
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Comparative Examples la to lc
In each of the Comparative Examples la to lc, the muddy
water as used in Examples lA to lL was treated in the same manner
as in Examples lA to lL except that the chemicals 1 and 2 used in
Examples lA to lD were not used.
In each of Comparatives Examples la to lc, the
concentration ~%) of fine particles in the muddy water, the amounts
(%) of the respective chemicals per 100 ml of the muddy water, and
water content (%) in the separated flocs, turbidity of separated
water and the state of flocs (filter cake) are shown in Table lB.
The chemicals 3 and 4 were added as aqueous solutions of 20% and
0.2%, respectively. The pH after addition of the chemical 3 was
7.1 to 7.3.
As a result, it was found that the separated water
obtained in each of Comparative Examples la and lb were turbid. In
Comparative Example lc, the anionic polymer coagulant had to be
added in an amount larger than in Examples lA to lL and Comparative
Examples la and lb.
Comparative Examples 2a to 21
In each of Comparative Examples 2a to 21, aluminium
sulfate was added as chemical 1 to a muddy water (muddy water
having a concentration of 35~) as used in Examples lA to lL, so
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that the pH of the muddy water is adjusted to value indicated in
Table 2. Immediately, in each of Comparative Examples 2a, 2c, 2e,
2g, 2i and 2k, a partial hydrolyzate of polyacrylamide having a
molecular weight of about 107 (anionic polymer coagulant, commercial
name DK Floc DK-101 available from Kurita Kogyo Kabushiki Kaisha)
was added as chemical 2. Instead of the chemical 2, in each of
Comparative Examples 2b, 2d, 2f, 2h, 2j and 21, a polyacrylamide
having a molecular weight of about 107 (a nonionic polymer
coagulant, commercial name EDP Floc 151 available from Kurita Kogyo
Kabushiki Kaisha) was added as chemical 3.
The chemicals 1, 2 and 3 were, respectively, used as
aqueous solutions having concentrations of 20%, 0.2% and 0.25%.
During the addition of the respective chemicals, the muddy water
were agitated.
In each of Comparative Examples 2a to 21, the
concentration (%) of fine particles in the muddy water, the pH of
muddy water after addition of the chemical ~ and the amounts (%) of
the respective chemicals per 100 ml of the muddy water are shown in
Table 2.
The water content (%) in flocs separated by filtrating
the coagulated muddy water, turbidity of the separated water and
the state of flocs (filter cakes) are shown in table 2.
2~ From the above results, it was found that Comparative
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Examples 2a to 21 requires larger amounts of the anionic polymer
coagulant or nonionic polymer coagulant (chemical 2 or 3) than
Examples lA to lL and Comparative Examples la to lc.
Comparative ExamPles 3a to 31
In each of Comparative Examples 3a to 31, muddy water as
used in Comparative Examples 2a to 21 but with a concentration of
26.6% was treated in the same manner as in Comparative Examples 2a
to 21 except that caustic soda was used instead of aluminium
sulfate as chemical 1. The chemicals 1, 2 and 3 were added as
aq~leous solutions having concentrations of 1.0%, 0.2% and 0.25%,
respectively.
In each of Comparative Examples 3a to 31, the
concentration (%) of fine particles in the muddy water, the pH of
the muddy water after the addition of the chemical 1 and the amount
(%) of the respective chemicals per 100 ml of muddy water are shown
in Table 3.
The water content (%) in flocs separated by filtrating
the coagulated muddy water, turbidity of the separated water and
the state of the flocs (cakes) are
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shown in Table 3.
As a result, it was found that in all Comparative
Examples 3a to 31, the anionic or nonionic polymer
coagulant (chemical 2 or 3) had to be used in amounts
larger than in Examples lA to lL and Comparative Examples
la to lc. The separated waters were turbid except for
Comparative Examples 3a, 3c and 3e. The turbidity of
the separated waters in Comparative Examples 3i to 31
was considerable.
Comparative Examples 4a to 4O
In each of Comparative Examples 4a to 4O,
aluminium sulEate was added as chemical 1 to the muddy
water used in Examples la to 11 (muddy water having
concentrations oE 10, 20 or 30%, so that the pH of the
muddy water is adjusted value indicated in Table 4.
Immediately, polyacrylamide having a molecular weight of
about 107 (nonionic polymer coagulant, commercial name
of EDP Floc 151 available from Kurita Kogyo Kabushiki
Kaisha) was added as chemical 2.
The chemicals 1 and 2 were, respectively, added
as aqueous solutions having concentrations of 20% and
0.25%. ~uring the addition of the respective chemicals,
the muddy water were agitated.
In each of Comparative Examples 4a to 41, the
concentration (%) of fine particles in the muddy water,
the pH after the addition of chemical 1 and the amounts
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(%) of the respective chemicals per 100 ml of the muddy water are
shown in Table 4.
The water content (%) of flocs separated by filtrating
the coagulated muddy water, turbidity o the separated water and
the state of flocs (cakes) are shown in Table 4~
As a result, it was found that in Comparative Examples 4a
to 41, the nonionic polymer coagulant (chemical 2) had to be added
in amounts larger than in Examples lA to lL and Comparative
Examples la to lc. The separate waters were turbid except for
Comparative Examples 4j, 4m and 4n~ In particular, the separated
waters in Comparative Examples 4a and 4k were considerable in
turbidity.
Com~arative Examp~es 5a to 5O
In each of Comparative Examples 5a to 5O, the muddy water
as used in Comparative Examples 4a to 4O was treated in the same
manner as in Comparative Examples 4a to 4O except that there were
used caustic soda as chemical 1 instead of an aluminium sulfate and
a partial hydrolyzate of polyacrylamide having a molecular weight
of about 107 (anionic polymer coagulant, commercial name of DR Floc
DK101 available from Kurita Kogyo Kabushiki Kaisha) as chemical 2
instead of the nonionic polymer coagulant.
The chemicals 1 and 2 where added as aqueous
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solutions having concentrations of 1~0% and 0.2%, respectively.
In each of Comparative Examples 5a to 50, the
concentration (%) of fine particles in the muddy water, the pH of
the muddy water after the addition of the chemical 1 and the
amounts (%) of the respective chemicals per 100 ml of the muddy
water are shown in Table 5.
The water content (%) in the flocs separated by
filtrating the coagulated muddy water, turbidity of separated water
and the state of flocs (cakes) are shown in Table 5.
As a result, it was found that in Comparative Examples
5a, 5b, 5f to 5j and 5m to 50, the separated waters were all turbid
with soft cakes. In Comparative Examples 5c to 5e, only small-
si~ed flocs were formed with bad solid-liquid separability.
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